فهرست مطالب

Scientia Iranica
Volume:27 Issue: 3, May-Jun 2020

  • Transactions on Civil Engineering (A)
  • تاریخ انتشار: 1399/04/10
  • تعداد عناوین: 14
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  • Alireza Entezami*, Hashem Shariatmadar, Abbas Karamodin Pages 1001-1018

    Feature extraction by time series modeling based on statistical pattern recognition is a powerful approach to structural health monitoring. Determination of an adequate order and identification of an appropriate model play prominent roles in extracting sensitive features to damage from time series representations. Early damage detection under statistical decision-making via high-dimensional features is another significant issue. The main objectives of this article are to improve a residual-based feature extraction method by time series modeling and propose a multivariate data visualization approach to early damage detection. A simple graphical tool based on Box-Jenkins methodology is presented to identify the most compatible time series model with vibration time-domain measurements. Furthermore, k-Means and Gaussian mixture model clustering techniques are utilized to examine the performance of the residuals of the identified model in damage detection. A numerical concrete beam and an experimental benchmark model are applied to verify the improved and proposed methods along with comparative analyses. Results will show that these approaches are successful in obtaining a sufficient order superior to a state-of-the-art order determination technique, generating uncorrelated residuals, extracting sensitive features to damage, and accurately detecting early damage by high-dimensional data.

    Keywords: structural health monitoring, statistical pattern recognition, feature extraction, time series modeling, residual extraction, unsupervised learning, Andrew plot, clustering analysis
  • Shiying Liu, Guojian Li *, Lin Xiao, Baohai Jia, Zhongyi Xu, Qiang Wang Pages 1019-1027

    It is crucial to control conductivity and optical transmittance of Al doped ZnO (AZO) thin films in application of optoelectronic materials. In this paper, AZO thin films are prepared by oxidizing thermal evaporated Zn-Al thin films in open air. Then, the effects of Al contents and film thicknesses on microstructure, optical and electrical properties of the AZO films are studied. The results show that the optical and electrical properties of the AZO films are affected by the Al content and thickness changing. The Haacke figure of merit reaches 2.91×10-4 Ω-1. The film surface morphology is changed by the Al content. Nanowire is formed when the Al content is 9.58%. The Al2O3 phase appears with an excessive Al content. The transmittance of the AZO films is less than 25% when the Al content is more than 9.58%. The grain size first increases and then decreases with the increase of film thickness when the Al contents remain at 2%. Within the limits of available transmittance, the sheet resistance and transmittance of the AZO thin film decrease exponentially with the film thickness increasing.

    Keywords: ZnO film, oxidation growth, vacuum evaporation, transparent electrode
  • Mehdi Derakhshandi *, Ghazale Rahmati, Mani Sadjadi Pages 1028-1038
    Recently, much effort has been devoted to improving the performance of geosynthetic reinforced walls under various stress conditions. In this research, the effect of using cemented mixed soil as a backfill material is studied on the static response of geosynthetic reinforced soil (GRS) walls. For this, numerical models based on a finite-difference code are made according to one of the Royal Military College’s (RMC) full scale test walls with a segmental facing. Different arrangements of soil reinforcement are considered in the presence of cemented sandy soil and sandy soil alone. In the cement-treated approach, each reinforcement layer is surrounded by a 30 cm cemented sand soil. The results show that using cement-treated sandy soil decreases the maximum deformation of the wall by as much as 75% compared with the case where untreated sandy soil is used. Moreover, by using cemented soil around reinforcements, the reinforcement forces reduce considerably. Therefore, increasing the number of reinforcement layers in the backfill will decrease the face wall deformation as well as the reinforcement forces, which are not cost-effective in many situations. It is also suggested that using the cement-treated technique can be an efficient cost-saving method compared with common GRS walls.
    Keywords: geogrid, Reinforced retaining walls, Cement-treated soil, Numerical model, Parametric analysis
  • R. Guo * Pages 1039-1049

    The rutting deformation not only shortens the service life of asphalt pavement, but also brings great risks to the drivers. The rutting resistance of Stone Matrix Asphalt (SMA) is affected by many factors. This study aims to thoroughly discuss the main factors of rutting resistance and establish the dynamic stability prediction model that based on the experimental data from Marshall testing and wheel tracking test in SMA mixtures. The results show that the optimal dosage bitumen of rutting test is 0.1~0.3% more than that of Marshall testing in SMA mixtures. With the temperature increases 0.5℃, the dynamic stability of SMA mixtures decreases by an average of 18.6%. The more amount of aggregate and mineral powder donnot mean the better rutting resistance in SMA mixtures. It causes to reduce the rutting resistance of SMA mixtures as compaction work is too much or too little. There is a positive correlation between the dynamic stability of SMA mixtures and fractal dimension, relative coefficient and asphalt content, while it is a negative correlation between the dynamic stability of SMA mixtures and rolling times, testing temperature.

    Keywords: Road engineering, Rutting resistance, Influencing factors, Stone matrix asphalt, Prediction model
  • A. Gholamrezatabar*, B. Ganjavi, G. Ghodrati Amiri, M.A. Shayanfar Pages 1050-1065

    It is well recognized that structures designed by conventional seismic design codes experience large inelastic deformations during strong ground motions. Realistic estimation of force distribution based on inelastic response is one of the important steps in a comprehensive seismic design methodology in order to represent expected structural response more accurately. This paper presents an extensive parametric study to investigate the structural damage distribution along the height of the steel moment-resisting frames (SMRFs) designed based on the stat-of-art constant-ductility performance-based plastic design (PBPD) approach considering soil flexibility effects when subjected to 20 strong ground motions. To this end, the effect of fundamental period, target ductility demand and base flexibility level are investigated and discussed. Based on the numerical results of this study, simplified equations are proposed for practical purpose to refine and modify the lateral force distribution pattern already suggested by researchers based on the study of inelastic behavior developed for fixed- and flexible-base structures by using relative distribution of maximum story shears of the selected structures subjected to various earthquake ground motions. It is demonstrated that the proposed equations can be adequately estimated the optimum values of shear proportioning factor for both fixed-based and soil-structure systems.

    Keywords: Seismic design lateral force, Performance-based plastic design, Steel moment structures, Soil-structure interaction, optimum shear proportion factor
  • Riaz Bhanbhro *, Roger Knutsson, Muhammad Auchar Zardari, Tommy Edeskär, Sven Knutsson Pages 1066-1074

    In an upstream tailings dam, loose layers might occur at different depths due to melting of frozen layers deposited during freezing temperature in Sweden. Reduced shear strength of such layers in a tailings dam might cause stability problems. Due to slow consolidation process, it is unknown, whether self-weight of a high tailings dam could have influence on strength and stiffness of soft tailings located at different depths. For numerical modelling, appropriate strength and stiffness properties of soft tailings are needed. For this purpose, loose layers in an upstream tailings dam were identified based on results of cone penetration tests. Consolidated Drained (CD) triaxial tests were conducted on undisturbed soft tailings collected from different depths of the dam. The results indicated that depth did not have considerable influence on strength and stiffness of tailings. Hardening Soil Model (HSM), at high confining pressures and axial strains underestimated stiffness of soft tailings under CD triaxial state. This study shows that: (i) proper care is needed in evaluating strength and stiffness parameters for soft tailings, and (ii) use of the HSM is likely to predict more deformations which could give an early warning before an actual failure of a tailings dam.

    Keywords: Soft tailings, Stress-strain behavior, Triaxial tests, Hardening Soil Model, strength, stiffness
  • Hamid Asadi Ghoozhdi*, Masood Mofid Pages 1075-1090

    Recently, a novel structural system, which is defined as damped outrigger system, has been proposed to control dynamic vibration of tall buildings. This paper examines seismic performance of tall buildings involving multiple outriggers equipped with viscous dampers. In this respect, a dual structural system (braced moment frame) is selected as a bare structure. In addition, the number and position of outriggers are assumed to be variable along the height of structure. Nonlinear response history analysis (RHA) is performed to evaluate the efficiency of damped-outrigger system under eight scaled ground motions. The results are presented based on the average of all ground motions. The mean inter-story drift ratio and maximum base shear force are compared in order to determine the best arrangement of damped outriggers. Conclusively, based on minimizing base shear force, the optimal location of damped outriggers under dynamic excitation is generally the same as that made for conventional outriggers. According to the inter-story drift ratio parameter, it is recommended to place one of the outriggers at the roof level.

    Keywords: Damped outrigger, Viscous Damper, Outriggers arrangement, High-rise steel structures, Inelastic dynamic time-history analysis
  • Mohammad Jalili Sadr Abad*, Mussa Mahmoudi, Earl Dowell Pages 1091-1112

    In this paper, an efficient computational solution technique based on the energy balance equations is presented for the dynamic analysis of shear-frames, as an example of a multi-degree-of-freedom system. After deriving the dynamic energy balance equations for these systems, a new mathematical solution technique which is called Elimination of Discontinuous Velocities is proposed to solve a set of coupled quadratic algebraic equations. The method will be illustrated for the free vibration of a two-story structure. Subsequently, the damped dynamic response of a three-story shear-frame which is subjected to harmonic loading is considered. Finally the analysis of a three-story shear-building under horizontal earthquake load, as one of the most common problems in Earthquake Engineering, is studied. The results show that this method has acceptable accuracy in comparison with other techniques, but is not only faster compared with modal analysis but also does not require adjusting and calibrating the stability parameter as compared with a method of time integration like the Newmark method.

    Keywords: Numerical Technique, Dynamic analysis, Shear-Frames, Energy Balance Equations, Coupled Equations, Elimination of Discontinuous Velocities
  • Alireza Sadat Hosseini, MohammadReza Bahaari *, Mohammad Lesani Pages 1113-1129

    The present article is dedicated to study of the effects of different parameters of fiber reinforced polymers (FRP), as strengthening material, on a tubular T-joint subjected to brace axial loading using finite element analyses. The effectiveness of FRP materials on enhancing the fatigue life of tubular T-joints was investigated through computing the ratio of the stress concentration factors (SCFs). FRP parameters which is considered include fiber orientation, FRP thickness, effective wrapping length and FRP material properties. The FRP materials were modeled and applied onto a basic numerical FE model which was validated in the past against well-known experimental results on weld-toe SCFs. Promising results were derived from the analyses showing that the FRP strengthening method can effectively decrease the SCF values for tubular T-joints.

    Keywords: Tubular T-joint, FRP, Strengthening, SCF, Finite Element
  • N.R. Malidarreh, I. Shooshpasha, S.M. Mirhosseini, Mehdi Dehestani * Pages 1130-1143
    Construction of structures on sandy soils of northern part of Iran encounters problems due to lack of proper strength properties. In recent years, bottles of Polyethylene terephthalate (PET) such as water bottles caused an environmental threat due to their prolonged persistence. Utilization of these materials for soil improvement seems to be a sustainable approach. In this study, the effect of recycled PET on mechanical properties of Babolsar sandy soil is investigated through an experimental program using direct shear and consolidated drained (CD) triaxial compression tests. Various contents of PET were added to sand with 3%, 5% and 7% cement contents. Curing time and relative density of samples were 7 days and 70%, respectively. Results showed that addition of fiber improves strength parameters such as cohesion and internal friction angle. Furthermore, the effect of the fiber is less marked with an increase in cement content. The samples with 3% cement demonstrated better results in both direct shear and tiaxial tests. By adding 0.5% and 1% PET fibers to the samples containing 3% cement at 100 kPa pressure, the ratio of strength in direct shear tests increased 13% and 24%, respectively, and in the triaxial test, it increased 50% and 93%, respectively.
    Keywords: Direct shear test, Triaxial test, polyethylene terephthalate fibers, reinforced sand, reinforced cemented sand
  • Eyubhan AVCI * Pages 1144-1161
    In this experimental study, the effect of curing temperature on the engineering properties of sand samples grouted with sodium silicate-glyoxal was investigated. The experiments were started with determination of the gelation times, viscosities and syneresis percentages of the blends prepared for injection, after which the injection experiments were then carried out at the determined mixing ratios. Grouted specimens were subjected to unconfined compressive strength (UCS) and permeability tests being kept at different curing temperatures (+10 °C, +20 °C and +30 °C) in the curing tank. As the temperature was increased, the viscosity values and gelling times decreased, while the syneresis percentages increased. The UCS of the grouted samples decreased with time. This decrease was observed to slow down in the samples kept at +10°C after the 56th day, while the same was on 28th day in those kept at +20°C and on 7th day for those kept at +30 °C. Also, UCS values decreased with the increasing temperature. The permeability values of the grouted samples decreased with time. This decrease has been observed to slow down after the 28th day. The increase in temperature reduced the permeability values.
    Keywords: Sodium silicate grouts, Curing temperature, unconfined compressive strength, Permeability
  • Siavash Salamatpoor, Yaser Jafarian *, Alborz Hajiannia Pages 1162-1175

    Adjacency and interfering of footings are a matter of importance in geotechnical engineering. The researchers have focused on the adjacency of the footings by several approaches, but the mechanism of nearby footings under unequal and non-simultaneous surcharges have not been explored to date. In this study, two series tests were conducted using small scale 1g models to investigate the behavior of the two adjacent footings under reinforced and unreinforced soil conditions. The footings were installed with different spacing and rested on loose saturate sand. The ultimate bearing capacity, settlement, and tilting of footings were evaluated when the footings are rested on unreinforced sand as well as the sand bed reinforced by concrete pedestals. The results indicate that reinforcing the new footing by three concrete pedestals in the spacing to footing's width ratio (S/B) of 0 (i.e., two coherent footings) results in 67% increase of the bearing capacity of the new footing compared to that of the unreinforced condition. Also, the settlement and tilting of the old footing adjacent to the new footing decrease respectively up to 250% and 600% in comparison to those of the unreinforced condition.

    Keywords: Strip footing, Sand, Pedestal, Settlement, Tilt, Bearing capacity, Model test
  • A. Kaveh *, Shima Bijari Pages 1176-1186
    In this paper, an efficient technique is proposed by displacement method of analysis and three metaheuristic algorithms consisting of the Colliding Bodies Optimization (CBO), Enhanced Colliding Bodies Optimization (ECBO) and Vibrating Particles System (VPS), for the simultaneous analysis and optimal design of truss structures. The presented method is applied to the minimum weight design of some planar and spatial truss structures. For examining the accuracy and efficiency of the proposed method, the problems are also designed by the same metaheuristic algorithms utilizing pure force method and pure displacement method as analysis tools (non-simultaneous) and the resulting structural weights are compared.
    Keywords: displacement method, metaheuristic algorithms, analysis, design, optimization, trusses, strain energy
  • Faramarz Moodi*, AliAkbar Ramezanianpour, Qasem Bagheri Chenar, Erfan Riahi Dehkordi Pages 1187-1195

    The current paper discusses the petrographic image analysis performed on core specimens that are extracted from a tunnel in the south west of Iran. During tunnel excavation, damages were observed in the inner sections of concrete segments. Due to field observations of damaged segments, environmental parameters and tunnel location, several damage scenarios were proposed. In order to assess damage mechanisms, 69 cores were extracted and a number of standard tests were carried out. Since chemical attacks alter microscopic properties of materials, petrographic image analysis was performed on five of the specimens to evaluate possible microscopic changes in concrete composition. The results show that petrographic image analysis is an efficient method to provide a profound insight into the effects of chemical attacks on concrete members.

    Keywords: Concrete durability, Petrographic image, Chemical attack, Sulfate, crack